A telephone network includes a hierarchy of switches for establishing a voice-data transmission path between a caller and a called party. Each party's telephone within a local area is coupled to a local switch. A plurality of local switches, encompassed within a larger area, are coupled to a toll switch. A plurality of such toll switches are then coupled to each other to provide connectivity between any two parties within a telephone system.
For example, referring to FIG. 1, basic components of a telephone network 100 for establishing such a voice-data transmission path include a caller telephone 102 coupled to a first local switch 104. The first local switch 104 is coupled to a first toll switch 106 via a first DCS (Digital Cross-connect System) 108. A called telephone 112 is similarly coupled to a second local switch 114. The second local switch 114 is coupled to a second toll switch 116 via a second DCS (Digital Cross-connect System) 118.
When the caller telephone 102 calls up the called telephone 112, a voice-data transmission path is established from the caller telephone 102 through the first local switch 104, through the first DCS 108, through the first toll switch 106, back through the first DCS 108, through the second DCS 118, through the second toll switch 116, back through the second DCS 118, through the second local switch 114, and finally to the called telephone 112.
A DCS (Digital Cross-connect System) has a plurality of local switches and a plurality of toll switches coupled thereto, and couples an appropriate local switch to an appropriate toll switch in establishing the voice-data transmission path. A local switch is coupled to a DCS via a toll-completing trunk group. A toll-completing trunk group is typically comprised of a plurality of toll-completing trunks as known to one of ordinary skill in the art of telephony. In FIG. 1, the first local switch 104 is coupled to the first DCS 108 via a first toll-completing trunk group 120. The second local switch 114 is coupled to the second DCS 118 via a second toll-completing trunk group 122. The toll switches are coupled to each other via an intertoll trunk group 124. An intertoll trunk group is typically comprised of a plurality of intertoll trunks as known to one of ordinary skill in the art of telephony. The intertoll trunk group 124 is coupled between the first DCS 108 and the second DCS 118.
Control data is used in inquiring about the availability of a voice-data transmission path. Such control data is sent to query the switches 104, 106, 114, and 116 regarding such availability. An STP (Signal Transfer Point) is coupled to each switch for receiving and transmitting such control data for each respective switch. In FIG. 1, a first STP (Signal Transfer Point) 130 is coupled to the first local switch 104, a second STP (Signal Transfer Point) 132 is coupled to the first toll switch 106, a third STP (Signal Transfer Point) 134 is coupled to the second local switch 114, and a fourth STP (Signal Transfer Point) 136 is coupled to the second toll switch 116. (Note, two STP's are coupled to each switch in a robust telephone network For example, the AT&T telephone network includes two STPs for each switch. However, it should be apparent to one of ordinary skill in the art that the present invention is not dependent on the STP configuration. Nevertheless, one STP per switch is shown in FIG. 1 for clarity of illustration.)
Referring to FIG. 2, a toll switch is coupled to a plurality of other toll switches and a plurality of local switches. As an example illustration, a predetermined toll switch 202 is coupled to a first local switch 204, a second local switch 206, and a third local switch 208, and switches a phone call originating or terminating in any of such local switches. The predetermined toll switch 202 is also coupled to a first toll switch 210 (which in turn is coupled to a fourth local switch 211), a second toll switch 212 (which in turn is coupled to a fifth local switch 213), and a third toll switch 214 (which in turn is coupled to a sixth local switch 215).
In the prior art telephone network, if any toll switch in the telephone network, such as the predetermined toll switch 202 were to fail, a spare toll switch 220 is at hand to take the place of the inoperative toll switch 202. A first broadcast satellite T/R (Transponder/Responder) 222 is coupled to the local switches 204, 206, and 208 that are coupled to the inoperative toll switch 202. The first broadcast satellite T/R 222 broadcasts data from these local switches 204, 206, and 208 to the spare toll switch 220, via a second broadcast satellite T/R (transponder/responder) 224. The second broadcast satellite T/R 224 also broadcasts data from the spare toll switch 220 to the local switches 204, 206, and 208.
This prior art technology for restoring operation to the telephone network in the event of a toll switch failure is cumbersome and costly. The spare toll switch 220, and the first and second broadcast satellite T/Rs 222 and 224 may be relatively costly to maintain, implement, and operate. Furthermore, connections between the numerous local switches to the first broadcast satellite T/R 222 via transmission facilities 226 and between the numerous toll switches to the spare toll switch 220 via additional transmission facilities 228 require additional costs. Moreover, the additional transmission facilities 228 from the toll switches 210, 212, and 214 to the spare toll switch 220 are typically utilized to full capacity only in the event of a failure at a toll switch. Furthermore, restoring operation to the telephone network by verifying proper operation of the spare toll switch 220 and the first and second broadcast satellite T/Rs 222 and 224 may be time-consuming.
Thus, a relatively more efficient and less-costly apparatus and method for handling a failure of a toll switch within a telephone network is desired.